The broad long-term objective of this research proposal is to establish heme oxygenase-1 (HO-1)-derived carbon monoxide (CO) as a novel and biologically important gas that regulates homeostasis at sites of vascular injury. We have measured the release of CO from vascular smooth muscle cells (SMC) and found that SMC-derived CO functions in an autocrine and paracrine fashion to inhibit SMC proliferation and platelet aggregation, respectively. The central hypothesis of this proposal is that HO-1-derived CO is a critical regulator of the SMC response to vascular injury. To test our hypothesis we plan to pursue the following three complementary and linked specific aims. In aim 1, we will examine the role of CO in regulating vascular SMC migration, collagen synthesis, and the secretion of vascular endothelial growth factor (VEGF) utilizing cultured vascular SMC. The effect of exogenously administered and endogenously derived CO will be studied. SMC will be exposed to CO via an exposure chamber while endogenous CO production will be induced by adenovirus-mediated transfer of the HO-1gene. The role of HO-1-derived CO in regulating SMC function will also be examined by harvesting SMC from the aorta of HO-1 knockout animals and comparing their functional properties with SMC from wild type animals. If CO is found to alter these SMC functions, we will determine the involvement of the cGMP or p38 mitogen activated protein kinase signaling pathways. In aim 2, we will elucidate the actions of HO-1 in regulating collagen deposition and VEGF expression following arterial injury using transgenic mice deficient in HO-1. In addition, we will investigate if CO inhalation can substitute for HO-1 in preventing collagen deposition and VEGF expression in these animals. In aim 3, we will explore the effect of adenovirus-mediated HO-1 gene delivery on collagen accumulation and VEGF expression in these animals. Finally, we will determine if CO-mediated VEGF release functions in a paracrine manner to stimulate endothelial cell growth both in vitro and in vivo. It is anticipated that these studies will (a) establish CO as a novel regulator of the vessel wall's response to injury and (b) implicate the HO-1/CO system as a promising new therapeutic target in treating vascular fibroproliferative disease.